Polymeric media with fibers having diameters of approximately 2 to 20 microns can be utilized to provide air filtration. The efficiency of such media in the collection of fine airborne particulates, especially airborne particulates in the range of 300 nanometers to 1 micron diameter (the so called E1 Group), can be enhanced by the addition of a nanofiber web layer atop the media. These nanofibers typically have diameters of approximately 50 to 2,000 nanometers on up to about 2 microns and are most commonly produced by electrospinning, which deposits them as a random web upon the media where they bridge openings in the media.
As applied, the nanofiber web is quite fragile in that it is bound to the substrate only by weak electrostatic and van der Waals forces. Prior proposals have utilized a thin protective scrim layer, adhesives, elevated media temperature, or a combination of these approaches to enhance the bonding. As will be explained below, each of those approaches either adds significant cost or increases airflow resistance or undesirably changes the media morphology. Disclosed is a novel method of nanofiber bonding that overcomes many of the prior art shortcomings.